We describe the development of chain-growth condensation polymerization for the synthesis of well-defined pi-conjugated polymers via a new polymerization mechanism, catalyst-transfer polymerization. We first studied the condensation polymerization of Grignard-type hexylthiophene monomer with a Ni catalyst as a part of our research on chain-growth condensation polymerization, and found that this polymerization also proceeded in a chain-growth polymerization manner. However, the polymerization mechanism involving the Ni catalyst was different from that of previous chain-growth. condensation polymerizations based on substituent effects; the Ni catalyst catalyzed the coupling reaction of the monomer with the polymer, followed by the transfer of Ni(0) to the terminal C-Br bond of the elongated molecule. This Catalyst-transfer condensation polymerization is generally applicable for the synthesis of polythiophene with an etheric side chain and poly(p-pheneylene), as well as for the synthesis of polyfluorene via the Pd-catalyzed Suzuki-Miyaura coupling reaction. (C) 2007 Wiley Periodicals, Inc.